"19 years ago tonight, I got to introduce you to #buffyannesummers (and #mrpointy too)," she captioned the '90s-era snap, in which she's wielding Buffy's signature weapon. "Thank you for taking the incredible journey with me and continuing still. I am and forever will be #grateful."

"12 years ago, I said
goodbye to a friend. It was an incredible journey that, I am so incredibly
proud of," she wrote at the time, including shots of her "Buffy"
co-stars David Boreanaz, Alyson Hannigan and Michelle Trachtenberg. "Thank
you all for joining me, and continuing to tell her story."

Sarah is
getting ready for another blast from the past as well.

The
38-year-old has been revealing behind-the-scenes peeks at the "Cruel
Intentions" TV remake, for which she's set to reprise her role as the
conniving brunette Kathryn Merteuil.